Mix the can of tuna with mayonnaise, salt and pepper and any other herbs or seasonings you`d like to add, walnuts taste good in it too- Be creative and have fun with it.,Put tuna mixture aside.,______,Over medium- low heat, saute the sliced mushrooms in olive oil until slightly crisp- I sometimes add left over chicken or a slice or 2 of bacon to the saute for variety.,Once the mushrooms are sauteed arrange them into a tidy little circle and place the tuna and mayo mixture very carefully onto the center of the mushroom platform- If you haven`t realized by now-- the mushrooms replace your bread.,Then place the tomato slice on top of the tuna and mayo, top it all off with cheese, reduce heat slightly, and cover for 1 minute or until the cheese is melted.,Carefully, with the aid of a flexible spatula, slide the tuna melt onto your plate- or a leaf of lettuce on your plate and enjoy.,Only 3 and a half carbs for the whole meal-- and it`s filling.,You can use other types of cheese and mushrooms or even more tomato, but take the carbs into account- some cheeses are higher than others and the same for veggies too.